Curve plotting and drafting instrument



NOV. :29, l g 5 K 2,138,494

CURVE PLOTTING AND DRAFTING INSTRUMENT Filed Nov. 21, 1936 V I; 4L 5 a vis f f 54' ii Mzwas B.K8wx,

Patented Nov. 29, 1938 UNE'EEB STTES OFFlE CURVE PLOTTING AND DRAFTINGINSTRUMENT 1 Claim.

My present invention relates to means for plotting and drafting curves,and more particularly aims to provide instrumentalities for that purposewhich are readily adjustable to suit requirements for numerous differentcurves, yet are simple in structure and inexpensive of manufacture.

In the drawing illustrating by way of example certain embodiments of theinvention,

Fig. 1 is a longitudinal edge View of one instrument in accordance withthe invention, appearing in its collapsed or non-use position;

Fig. 2 is a plan View of one fiat face or side of one element of theinstrument of Fig. 1, in similar condition as there;

Fig. 3 is a view similar to Fig. 2 of the other main element of theinstrument of Fig. 1;

Fig. 4 is an enlarged perspective of a holding member, slider or clipuseful with the instrument of my invention and forming a part thereof;

Fig. 5 is an enlarged end view of the instrument, showing a holdingmember in position thereon;

Figs. 6, 7, 8 and 9 are longitudinal edge views of the instrument ofFigs. 1 to 3, illustrating several different typical positions of use;

Figs. 10 and 11 are edge views corresponding to one end portion of Figs.1, the left in said figure, illustrating modified constructions, and

Fig. 12 illustrates one distinctive use position of the instrument ofFig. 11, supplemental to such positions as those of Figs. 6 to 8.

Referring to the drawing in more particular the instrument of myinvention, in its form as shown in Figs. 1 to- 9 by way of example,comprises a plurality of main elements, bars or strips, two beingillustrated in this instance, designated 53 and l l. These strip membersor columns are formed of any suitable material having an inherentelasticity permitting them to be flexed readily into such typicalpositions as shown in the figures, which positions it will be understoodare by no means the extremes or representative of the wide range ofcurvatures which may be obtained with the instrument. While the materialemployed is elastic and such as to afford the high degree of flexibilityindicated, the strips of the instrument also have a substantial inherentstifIness, so that they are self-sustaining in their various positionsof adjustment, and are susceptible of loading, either by way oflongitudinal Compression or tension, and in the several positions willretain each a regular smooth curvature characteristic of the positionand condition of loading, without introducing local irregularities.

One such material which I have found highly satisfactory for the purposeis a fairly high-grade tempered steel, in most cases a blued steel,having the general characteristics of that commonly used in themanufacture of flexible razor blades of the wafer type, but preferablysomewhat thicker or heavier. Other materials of the requisite charactermay be employed, however, including various compositions, such as phenolcondensation products, cellulosic compositions and others.

Turning again more particularly to Figs. 1 to 3 the strips l3 and M. asthere shown have corresponding ends provided with means forinterengaging them so as to limit relative lengthwise movement in atleast one direction. In the construction as in Figs. 1 to 9 I have shownfor this purpose one or more nibs or hooks I5 at the end of one strip,herein the member !3, two such hooks being illustrated in the presentinstance. They each comprise, as best seen in Fig. 1, a lateral portionand an extension or hook proper i5 These projections or hooks areadapted to be received in correspondingly located apertures l5, [6 inthe other strip member Hi.

In the collapsed or non-use position of the instrument, as in Fig. 1,the members 53 and I 4 are placed together flatwise, generally with theend formations l5 and I6 interlocked as illustrated. They may beretained in this position, and also in their various positions ofrelative adjustment as in the other figures to be referred to, bysuitable adjustable holding means adapted to be enaged with the stripsat various positions along them. For this purpose I preferably employone or more holding members in the nature of sliders or clips ll, one ofwhich is seen separately upon a larger scale in Fig. 4, and two or moreof which appear in various other figures such as Fig. 1. These clips orclamps IT as illustrated are onepiece elements of U-form having theirtwo legs so spaced as to fit accurately the combined thickness of thetwo or more main strips. Preferably these clamps or saddles ill havetheir side faces roughened, see Fig. 4, to assist in manipulating them,and the inner lower edge portions of the legs desirably are beveled asat i9, Figs. 4 and 5, as an aid in setting them onto the strip members.

The manner of operation of the instrument will be clear from aninspection of Figs. 6 to 9, showing several different typical usepositions. As is well-known to those familiar with mechanical drawing inits various fields of practical application, the usual draftingequipment for laying out curved lines comprises several different sizesof fixed curves and a few constant radius curves, with occasionally anadjustable curve of some relatively soft material that is bent, a partat a time, to fit a previously plotted curve. The use of these tools isusually slow, and oftenresults in irregular and uneven lines, dependingon the compensating skill of the draftsman. The flexible curves of theprior art such as referred to, which are bent and fitted by repeatedhand manipulation to conform to the required curve, and which are heldin place by weights or otherwise, are unsatisfactory, particularly forcurves other than long fiat curves of substantial radius. Where a lineis desired which is symmetrical about some axis on the paper the priordevices such as referred to frequently complicate the operations insteadof simplify them, and it is dimcult or substantially impossible toduplicate the half of a symmetrical curve accurately. With theinstrument of my invention, it will be observed that the device itselfserves to plot the desired curve, as contrasted with the localizedbending of the previous devices until an approximation of the desiredcurve is reached by the trial and error method.

In obtaining this result of self-plotting or selfadjustment I avail ofthe principle that the elas tic failure of a uniform or symmetricalcolumn results in the formation of a smooth symmetrical curve. If theloads imposed are below the elastic limit of the material no damageresults to the column, and the removal of the load allows the latter toassume its original position. In the instrument of my invention, elasticfailure is obtained by loading the two or more parallel columns orstrips in opposition to each other, usually in such way that one elementis in compression and the other in tension. The resulting curves dependupon the degree of loading and the nature of the interengaging oranchoring means for the ends of the columns. Where the holding iseffected susbtantially at the extreme end of the compressed member, asfor example at the left in Fig. 6, the resulting curve has no point ofinflection. A similar result is obtained with the form ofinterengagement illustrated in Fig. 10 in which one of the strips,designated M has its end turned over to provide in effect an end pivot22 bearing in a similar turned portion or hinge 23 of the other memberl3. If then the opposite ends, or portions of strips remote from theinterengaged ends are restrained, as by application of holding meanssuch as the sliders H, in the manner as at the right in Fig. 6, onereversal of curvature results at said restrained end. When the other orfirst ends are similarly restrained, as in Fig. '7, two reversals ofcurvature result.

Loading such as here referred to may be obtained simply by moving orsliding one or both ends of one column in-board with respect to the endor ends of the other, and securing the members in such position. The twoor more strips or columns then function as a unitary instrument and caneasily be manipulated and held in place on the drawing board, usually bybut one hand of the draftsman.

Fig.- 6 is typical of one family of non-symmetrical curves. To formthem, starting from the collapsed position of the instrument as in Fig.1, one of the slider clips il generally is removed. The two main membersor strips l3 and M may then be moved relatively, by drawing or pushingone member through the remaining clip, while holding the other. Havingmade in this manner an approximate adjustment to the desired curve, afiner adjustment can then readily be made by properly applying a secondclip I1 in-board of the first one, as shown in Fig. 6.

A large family of symmetrical curves may be obtained in the mannerillustrated in Fig. '7, merely by applying the clips ll, I! at both endsof the curve, which accordingly will have two regions of inflection, oneadjacent each restraining point or clip. Other related curves of thesame general families may be obtained by bringing the two columns orstrips together at an intermediate point, as illustrated for example inFig. 8. In this particular instance one of the resulting curves, at theright in said figure, is symmetrical, having inflection points at bothends, adjacent the clips, similarly as in Fig. 7; the other curve, atthe left in Fig. 8, is non-symmetrical, similarly as in Fig. 6. It willbe understood that two or more symmetrical curves may similarly beobtained by applying one or more additional clips in Fig. 8, forexample, adjacent the left or pinned ends of the members I3 and M. Inconnection with each of Figs. 6, '7 and 8 it will be noted that themember which is under tension and which receives the least curvature,namely the strip Hi in said figures, also describes a curve of which usemay be made in drafting, the curve in Fig. 6 being non-symmetrical,symmetrical in Fig. '7, and part symmetrical and part non-symmetrical inFig. 8.

A still different family of relatively long and fiat curves may beobtained in the manner as illustrated in Fig. 9. In this case the stripsI3 and M are interengaged at their left ends but With the strip l3reversed so that the hook turns in toward the other strip l4, oppositelyfrom its position as in Fig. 1 and the others. In this instance themembers are oppositely curved, symmetrically with respect to each other,but are individually non-symmetrical.

The dimensions of the columns or strip members l3, M will depend uponthe scale of the curves desired. The two members generally are of thesame or substantially the same length, but in some cases manipulation ofthe instrument is facilitated by having one strip somewhat longer thanthe other, particularly with instruments for the smaller scales ofcurves. Preferably the strip members, or one of them, are graduated orindexed upon one or both faces as indicated at 20, 2| in Figs. 2 and 3.The graduation unit may be arbitrary or any convenient dimension forexample, inch. Such scales or indices are convenient for use inresetting the instrument for the same curve as at some previous time,and in any instance the particular setting may be recorded for futurereference, memoranda being made, for example, that the zero point or endof strip B was set opposite point 3 on strip It, or that point 2 of thescale 20 of the strip l3 was set opposite point 5 of the scale 2| ofstrip 14.

In the modified construction illustrated in Fig. 10, previouslydescribed, each of the types of curves may be had as in connection withthe form of the previous form, such as illustrated by way of example inFigs. 6, '7, 8, with the exception of the positioning illustrated inFig. 9. It should be noted that in both forms the two main strip membersare bodily separable, those of Fig. being separated by sliding the pinelement 22 of strip [3 sidewise out of the hinge 23 of the other member.This allows of either of the strips being used separately as a straightedge, or either of them may be bent back upon itself and clamped in alooped position, producing a new family of curves characterized by a.somewhat greater curvature than those illustrated.

In Figs. 11 and 12 I have illustrated another construction in which thestrip members W and I M are pinned or pivoted together flatwise as bymeans of the rivet 24. Such construction will not give the curves havingone relatively steep side, such as illustrated in Fig. 6, but it has theadvantage that the two strips may be swung oppositely into open orextended position and their opposite ends bent back and overlapped andsecured, in the manner illustrated in Fig. 12, thus producing a totalcurve approximating or coinciding with a true circle. Similar resultsmay be obtained with the instrument of Figs. 1 to 9 by separating thetwo elements, extending them into prolongation of each other,overlapping adjacent ends and securing them with a clip l1, and thenflexing the opposite ends of the resulting extended strip toward eachother into substantially circular or hoop form in which they may be heldby clamping together the overlapped end portions. The same is true withthe form of Fig. 10. Still other families of curves may be obtained withthe instrument of any of the figures by swinging the free ends of thetwo strips laterally away from each other, while leaving the pinned orinterlocked ends in engagement, and carrying the free ends of the twostrips entirely around into overlapping relation, in which they may besecured by the clips, with resulting ovate, guttiform, cordate, piriformand other varieties of curves and figures.

As previously pointed out, a relatively inexpensive and easilymanufactured instrument may be made with the use of a good grade ofsteel as the material for the columns or strips, but the invention isnot limited as to the particular material employed. While I have shownbut two strip members by way of illustration, it will be understood thatthe instrument in any given case may be composed of a greater pluralityof such members, depending upon the elasticity necessary for theparticular curve required. The strip members also have been illustratedas of the same thickness and cross sectional shape throughout but insome instances one or more of the strips may be provided with a uniformor symmetrical taper, or one strip may be somewhat thicker or stiiferthan the other, again depending on the type of curve to be produced. TheU-shaped sliders or clamps illustrated have proved eificient as theholding means, particularly with the smaller sizes of instrument, but itwill be understood that if desired I may employ a clamp equipped with aset-screw which may be turned up into securing position when the propercurve has been obtained, or means of the rack and pinion type may beemployed in association with the movable holders, to facilitate settingof the instrument.

My invention is not limited to the particular embodiments thereofillustrated and described herein, and I set forth its scope in myfollowing claim.

I claim:

A manual curve-plotting and drafting instrument comprising a pair ofsimilar normally fiat elongated strip members each having a similarthickness of but a small fraction of their width and each being ofsubstantial rigiditycrosswise their flat faces but each similarlyelastically flexible in the direction of their length, said stripmembers having a normal or non-use position wherein they lie fiatwiseone against the other in compact closed relation substantially as aunitary ruler-like device, interengaging formations at a correspondingend of each strip member for interconnecting them and limitinglongitudinal movement of one member relative to the other at least inone direction at said ends, and one or more clip-like holding elementsfor adjustably clamping together said strip members at a like number ofpoints spaced from their interengaged ends thereby to hold the stripmembers in various flexed positions of relative curvature into whichthey may be manipulated for curve-plotting and drafting purposes.

THOMAS B. KNOX.

